Unsymmetrically Substituted 1,1′-Biferrocenylenes Maintain Class III Mixed-Valence Character

Abstract

UV−vis−near-IR electronic absorption spectra of unsymmetrically substituted derivatives of 1,1′-biferrocenylene (bis(fulvalene)diiron = BFD) have been systematically evaluated upon oxidation using spectroelectrochemical techniques. Upon reversible electrochemical oxidation to the BFD + monocation and BFD 2+ dication state, the characteristic intervalence chargeresonance (IVCR) transitions of a class III mixed-valence system in solution state was confirmed. The class III mixed-valence character of the parent BFD + system was not altered upon unsymmetric substitution. Peak-fit analysis and TD-DFT calculations were utilized to assign the observed IVCR transitions.

Ferrocenyl‐Pyrenes, Ferrocenyl‐9,10‐Phenanthrenediones, and Ferrocenyl‐9,10‐Dimethoxyphenanthrenes: Charge‐Transfer Studies and SWCNT Functionalization

“…[85,92] To investigate this behavior,p ropylene carbonate (m = 4.9 D) was further chosen as an additional solvent for the spectroelectrochemical measurementso f12.A nalogous investigations on 5b failed in the UV/Vis/NIR setup, owing to its insufficient solubilityi np ropylene carbonate.I n the case of [12] + ,t he IVCT transition could be detecteda ta pproximately 11 000 cm À1 by using the solventw ithh igherp olarity,r evealing as olvatochromic shift (Dn max )o f1 000 cm À1 (Table 4, Figures SI24 and SI25 in the Supporting Information). The magnitude of Dn max in comparison for very strongly coupled systems (Dn max % 100 cm À1 ) [93] confirms ac lass II classification accordingt oR obin and Day. [91] To gain ad eeper insighti nto the communication between the aromatic core andt he ferrocenyl ligands, the ligand-tometal charge transfer properties of 3, 5a,b, 7a,a nd 12 were investigated, except for 10,w hich showed aM LCT ( Figure SI23 in the SupportingI nformation).…”

“…In the case of [ 12 ] + , the IVCT transition could be detected at approximately 11 000 cm −1 by using the solvent with higher polarity, revealing a solvatochromic shift (Δ ν max ) of 1000 cm −1 (Table , Figures SI24 and SI25 in the Supporting Information). The magnitude of Δ ν max in comparison for very strongly coupled systems (Δ ν max ≈100 cm −1 ) confirms a class II classification according to Robin and Day …”

Substituent Influence on Charge Transfer Interactions in α,α′-Diferrocenylthiophenes

“…During the oxidation of 1 – 8 typical absorptions in the UV–vis (inner ferrocenyl related π–π* and MLCT/d–d transitions) and near-IR regions appear as mixed-valent 1 + – 8 + are formed (Table ). ,,,, Within the near-IR region a high energy near-IR absorption around 10000 cm –1 can be assigned to a ligand to metal charge transfer transition (LMCT), as reported previously. ,− ,,,, Intervalence charge transfer (IVCT) transitions were observed in the spectral range between 4000 and 5000 cm –1 together with further low-energy near-IR absorptions (Table ) . These transitions are often explained with charge transfer assisted ligand field (LF) or LMCT interactions; moreover, the bandwidth at half-height (Δν 1/2 ) for these relatively intense absorptions is more narrow than the Hush theory would predict (Δν 1/2 (theor)) for an IVCT transition. ,,− Additionally, those bands are often called interconfigurational (IC) transitions (dπ–dπ). ,, However, Warratz et al have proposed an IVCT character for such absorptions in mixed-valent nonbridged biferrocene species, similar to what is known for bis(fulvalene)diiron systems. − …”

Effect of Large Electrolyte Anions on the Sequential Oxidations of Bis(fulvalene)diiron Attached to Glassy Carbon by an Ethynyl Linkage

“…These trends indicate that the electronic effects accompanying the oxidation of ethynyl-BFD are very similar to those of both BFD itself and bis­(fulvalene)­dinickel. We conclude that E-BFD + , like the parent BFD + , has its positive charge equally distributed on the two “ferrocenyl” halves of the molecule, a model that is consistent with spectroscopic and calculational results on other monosubstituted BFD + systems …”

“…We conclude that E-BFD + , like the parent BFD + , has its positive charge equally distributed on the two "ferrocenyl" halves of the molecule, a model that is consistent with spectroscopic and calculational results on other monosubstituted BFD + systems. 66 When one equivalent of n-BuLi is added to a THF solution of either E-BFD isomer, a chemically irreversible anodic feature appears at a less positive potential than E 1/2 (1), owing to oxidation of the lithioethynyl complex, LiE-BFD, formed in solution (eq 8). 67 As the potential scan is continued positive, the reversible E-BFD 0/+ couple is observed (Figure 3).…”